Apollo Service Module Oxygen Tank Apollo Service Module Oxygen Tank A simplified cross-section of oxygen tank 2 and its location within Apollo 13’s Command and Service Module. The capacitance gage (left vertical tube) served to feed and drain liquid oxygen in and out of the tank. The heater and fans (right vertical tube) were powered by insulated electrical wiring fed in through the capacitance gage. A spark from this damaged wiring ignited the liquid oxygen and the Teflon insulation inside the tank, causing a rapid build-up of pressure that blew out the panel and seriously damaged the spacecraft. NASA / Casey DreierSource diagrams: Report of the Apollo 13 Review Board (PDF).